Podcast Producer uses an object tag with a classid attribute to embed
QuickTime Player into a page. In r70748, we changed our behavior to
render the object's fallback content when a non-empty classid is
encountered, per HTML5. Since Podcast Producer videos have no fallback
content, this change in behavior causes the video to fail to load.

Since the object tag has a valid type attribute, we would be able to
load it if weren't for the non-empty classid. This patch changes our
policy to allow objects with non-empty classids if there is no fallback
content. We still continue to prefer fallback content if it exists,
however.

* html/HTMLObjectElement.cpp:
(WebCore::HTMLObjectElement::hasValidClassId): Treat a non-empty
classid as valid if the object has no fallback content.